1. Field of the Invention
This invention relates to an improved atomizer for providing very small, uniformly-sized liquid particles. More particularly, it relates to such an atomizer especially adapted for providing such liquid particles in a wind tunnel for the purpose of seeding air flow in the wind tunnel for laser Doppler velocimetry.
2. Description of the Prior Art
A variety of atomizers for providing a stream of finely divided liquid particles are known in the art. For example, such liquid atomizers are disclosed in the following issued patents: U.S. Pat. No. 536,216, issued Mar. 26, 1895 to Luther et al.; U.S. Pat. No. 3,774,842, issued Nov. 27, 1973 to Howell and U.S. Pat. No. 4,221,339, issued Sept. 9, 1980 to Yoshikawa.
It is conventional practice for analyzing airflow patterns around airfoils and other structures in wind tunnels to utilize small particles dispersed in the airflow to scatter light to make the flow patterns visible. The scattered light is measured with sophisticated instruments, such as a laser Doppler velocimeter (LDV), to analyze the flow patterns. An example of such an LDV instrument is disclosed in U.S. Pat. No. 3,915,572 issued Oct. 28, 1975 to Orloff. Inaccurate LDV measurements are obtained when the particles are non-uniform in size and when they fail to move in synchronism with the airflow. Attempts to utilize commercially available atomizing nozzles for producing the small particles from a liquid have produced unsatisfactory results. The atomized mist obtained with such commercially available nozzles contains large droplets, and the spatial distribution obtained with such nozzles causes the deposition of particles on windows in the wind tunnel used for the LDV observations. If the droplets are seeded with solid particles and the droplets are too large, the liquid will fail to evaporate before the particles reach the test section. Evaporation failure can permit the existence or growth of droplets with more than one solid particle therein. These enlarged droplets will produce a false measurement when illuminated by the laser beam of a LDV. Further, it is conventional practice in wind tunnel construction to provide porous metal suction panels on the sides of the wind tunnel to thin sidewall boundary layers to reduce airfoil interference effects. If the atomized mist is allowed to reach these porous panels, the panels will become clogged and will require removal for cleaning. Such commercial atomizer nozzles are also too large for insertion through a limited access port of a wind tunnel inlet. A need therefore still remains for a liquid seeding atomizer particularly suited for the wind tunnel environment.